Wafer inspection and metrology systems help a semiconductor manufacturer increase and maintain integrated circuit (IC) chip yields by detecting defects that occur during the manufacturing process. One purpose of inspection and metrology systems is to monitor whether a manufacturing process meets specifications. Inspection and metrology system can indicate the problem and/or the source of the problem if the manufacturing process is outside the scope of established norms, which the semiconductor manufacturer can then address.
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
Semiconductor wafers can include thin films, such as oxides or nitrides, which may be less than 1 nm to several μm in thickness. On a wafer, the thin film may be present on the front surface (which typically includes additional layers or semiconductor devices), back surface opposite of the front surface, or an edge between the front and back surfaces. Chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and epitaxy are four techniques that can be used to form such a thin film, but others are possible.
The thickness of these thin films can affect device performance or yield. Semiconductor manufacturers typically want to inspect or measure the thin film and, in particular, determine thickness and properties of the thin film. However, determining thickness and, for example, optical properties can be challenging. This is especially true for thin films present on the edge or back surface of a semiconductor wafer. Currently, there is no method to do metrology on the back surface of a wafer, especially when the front surface is patterned and cannot be placed on a wafer chuck. There also is no method to provide “all wafer surface metrology,” or metrology on all surfaces of the wafer. In particular, no technique can provide back surface film metrology in manufacturing environment. Therefore, what is needed is improved metrology hardware techniques.